To evaluate and compare exposure to diesel and biodiesel emissions and acute health effects in underground mining. Background: Despite mine ventilation and emission controls, underground miners are exposed to concentrations of diesel exhaust that frequently exceed the MSHA standard of 160 g/m3 for diesel particulate matter. A known carcinogen, diesel emissions have also been linked to a broad range of respiratory and cardiovascular health effects, both acute and chronic. Recently, use of biodiesel fuel as a blend with diesel fuel has been promoted as a means of reducing particulate exposure. However, there have been no studies evaluating the health effects of exposure to emissions from equipment running on diesel fuel as compared with a biodiesel blend, and some in vitro studies suggest greater toxicity from biodiesel use. Specific aims: 1) Evaluate inhalation exposures associated with use of diesel and biodiesel blend-fueled equipment in an underground mine; 2) Evaluate health effects and biomarkers of altered physiology associated with exposure to emissions generated using diesel and biodiesel blend-powered equipment; and 3) Compare the differences in health effects and biomarkers of altered physiology associated with exposure to diesel and biodiesel blend emissions. Study design: Using a cross-over experimental design alternating use of diesel and 50% biodiesel/diesel blend (B50) fuels, mining and mineral engineering students operating a load-haul-dump vehicle in an underground mine will be monitored for exposure to contaminants and health effects. Respirable dust, elemental carbon, black carbon, nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), aldehydes, and polycyclic aromatic hydrocarbons (PAHs) will be sampled from the mine. Spirometry, symptoms, sputum, blood, urine, exhaled breath and ultrasonography will be collected on all subjects pre- and post-exposure. Inflammatory markers and markers of oxidative stress, including interleukin (IL)-6, -8 and -10, myeloperoxidase (MPO), and matrix metalloproteinase-9 (MMP-9) will be analyzed in induced sputum. Blood will be analyzed for mediators of vascular damage including P-selectin and endothelin-1 (ET-1). Urinary 8- hydroxy-2'-deoxyguanosine (8-OHdG) will be assayed to assess oxidative DNA damage. Exhaled nitric oxide (NO), a marker of airway inflammation, and exhaled carbon monoxide (CO), a marker of CO exposure will both be evaluated. Ultrasound of brachial flow-mediated dilation will be used to evaluate changes in vascular endothelium function. The paired differences in pre- and post-exposure biomarkers of effect will be compared for exposures to diesel and B50 biodiesel. For each fuel type, regression analysis will be used to model the effects of emissions contaminants on pre- to post-exposure changes in individual biomarkers. Relevance to public health: This study will help determine the health consequences of use of biodiesel fuel blends in the underground mining setting. Information on the health effects of conversion to biodiesel fuels in occupational and environmental settings will also help to inform future policy decisions.